4 Genetic information, variation and relationships between organisms EQs

Question 1

Give the two types of molecule from which a ribosome is made (2 marks)

Answer 1

RNA and Protein

Question 2

Describe the role of tRNA in the process of translation (3 marks)

Answer 2

1. Anticodon complementary to codon
2. specific amino acid transferred to ribosome,
3. correct sequence of amino acids polypeptide

Question 3

Describe the role of a ribosome in the production of a polypeptide (3 marks)

Answer 3

1. mRNA binds to ribosome,
2. tRNA with complementary anticodon forms base pairs with the mRNA codon as there are two binding sites
3. peptide bond forms between amino acids via condensation reaction
4. moves along to next codon

Question 4

Give two differences between structure of mRNA and tRNA (2 marks)

Answer 4

1. mRNA does not have hydrogen bonds, tRNA does
2. mRNA is linear, tRNA is cloverleaf

Question 5

What is the proteome of a cell? (1 mark)

Answer 5

Range of different proteins that a cell is able to produce

Question 6

Describe how a phosphodiester bond is formed between two nucleotides within a DNA
molecule. (2 marks)

Answer 6

1. Condensation reaction
2. Between phosphate and deoxyribose
3. Catalysed by DNA polymerase

Question 7

Name the protein associated with DNA in a chromosome. (1 mark)

Answer 7

Histone

Question 8

The nucleus and a chloroplast of a plant cell both contain DNA.
Give three ways in which the DNA in a chloroplast is different from DNA in the nucleus (3 marks)

Answer 8

In chloroplasts:
1.   DNA shorter
3.   DNA circular not linear
4.   Not associated with histones, unlike nuclear DNA

Question 9

Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide.
Give two reasons why. (2 marks)

Answer 9

1. Triplets code for same amino acid
2. Occurs in introns

Question 10

DNA is a polymer of nucleotides. Each nucleotide contains an organic base.
Explain how the organic bases help to stabilise the structure of DNA. (2 marks)

Answer 10

1. Hydrogen bonds between the base pairs holds two strands together
2. Many hydrogen bonds provides strength

Question 11

Suggest one advantage of showing the genetic code as base sequences on mRNA, rather than triplets on DNA. (1 mark)

Answer 11

Because ribosomes assemble polypeptides using mRNA code

Question 12

What name is given to a group of three bases on mRNA that codes for an amino acid? (1 mark)

Answer 12

Codon

Question 13

In a eukaryotic cell, the structure of the mRNA used in translation is different from the
structure of the pre-mRNA produced by transcription.
Describe and explain a difference in the structure of these mRNA molecules. (2 marks)

Answer 13

1. mRNA has no introns
2. because of splicing

Question 14

Why is the genetic code described as being universal? (1 mark)

Answer 14

In all organisms the same triplet codes for the same amino acid

Question 15

A scientist investigated possible relationship between air
pollution and the size of seeds produced by one species of tree.
He was provided with a very large number of seeds collected from a population of
trees in the centre of a city and also a very large number of seeds collected from a
population of trees in the countryside.
Describe how he should collect and process data from these seeds to investigate
whether there is a difference in seed size between these two populations of trees.
[5 marks]

Answer 15

1. Use random sample of seeds from each population
2. Use large enough sample to be representative of whole population;
3. Measure the mass
4. Calculate a mean and standard deviation for each population
5. Use the (Student’s) t-test;
6. Analyse whether there is a significant difference
   between the means of the two populations;

Question 16

Describe how a gene is a code for the production of a polypeptide. (3 marks)

Answer 16

1. Because base sequence;
2. In triplets
3. Determines order of amino acid sequence

Question 17

Define the term exon (1 mark)

Answer 17

Base coding for sequence of amino acids

Question 18

What are three differences between DNA in the nucleus
of a plant cell and DNA in a prokaryotic cell? (3 marks)

Answer 18

1. Introns v no introns;
2. Linear v circular;
3. No plasmids v plasmids;

Question 19

Define ‘non-coding base sequences’ and describe where the non-coding multiple repeats are positioned in the genome. (2 marks)

Answer 19

1. DNA that does not code for sequences of amino acids.
2. Positioned between genes

Question 20

Suggest one way the structure of the chromosome could differ along its length to result in the stain binding more in some areas. (1 mark)

Answer 20

Differences in base sequences

Question 21

What is a homologous pair of chromosomes? (1 mark)

Answer 21

Two chromosomes that carry the same genes

Question 22

Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation. (3 marks)

Answer 22

1. tRNA brings specific amino acid to ribosome
2. Anticodon on tRNA binds to codon on mRNA
3. Amino acids join by condensation reaction to form peptide bond

Question 23

Describe how mRNA is produced from an exposed template strand of
DNA. (3 marks)

Answer 23

1. Free RNA nucleotides form complementary base pairs
2. Phosphodiester bonds form
3. By action of RNA polymerase;

Question 24

Describe how mRNA is formed by transcription in eukaryotes. (5 marks)

Answer 24

1. Hydrogen bonds between DNA bases break;
2. Only one DNA strand acts as a template;
3. Free RNA nucleotides align by complementary base pairing;
4. In RNA Uracil base pairs with adenine on DNA
5. RNA polymerase joins adjacent RNA nucleotides;
6. By phosphodiester bonds
7. Pre-mRNA is spliced to form mRNA

Question 25

Describe how a polypeptide is formed by translation of mRNA. (6 marks)

Answer 25

1. mRNA attaches to ribosomes 2. tRNA anticodons bind to complementary mRNA codons 3. tRNA brings a specific amino acid 4. Amino acids join by peptide bonds 6. tRNA released after amino acid joined to polypeptide 7. The ribosome moves along the mRNA to form the polypeptide

Question 26

What does degenerate mean? (1 mark)

Answer 26

More than one codon codes for a single amino acid

Question 27

Explain how non-disjunction mutation changes the number of chromosomes (2 marks)

Answer 27

1. In meiosis 2. Chromosomes don't separate

Question 28

Apart from mutation, explain one other way genetic variation within a species is increased. (2 marks)

Answer 28

1. Random fusion of gametes 2. Produces new allele combinations

Question 29

Explain how the chromosome number is halved during meiosis. (2 marks)

Answer 29

1. Homologous chromosomes pair 2. One of each pair goes to each daughter cell / to opposite poles;

Question 30

Describe the process of crossing over and explain how it increases genetic diversity. (4 marks)

Answer 30

1. Homologous pairs of chromosomes associate 2. Chiasmata form 3. Equal lengths of non-sister chromatids 4. Producing new combinations of alleles;

Question 31

Explain why all the cells of the body will have this mutation. (2 marks)

Answer 31

1. All cells derived from a single cell by mitosis; 2. Mitosis produces genetically identical cells

Question 32

What is meant by ‘species richness’? (1 mark)

Answer 32

A measure of the number of different species in a community;

Question 33

Suggest one consideration the scientists had taken into account to make sure their method allowed them to identify accurately the species to which each belonged. [1 marks]

Answer 33

Use photographs / use a key

Question 34

Give two ways the students would have ensured their index of diversity was representative of each habitat. (2 marks)

Answer 34

1. Random samples; 2. Large number of samples

Question 35

Suggest why biodiversity decreases when farmers use larger fields. (1 mark)

Answer 35

Fewer species

Question 36

Farmers are now being encouraged to replant hedges on their land. Suggest and explain one advantage and one disadvantage to a farmer of replanting hedges on her farmland. (2 marks)

Answer 36

Advantage - 1. Greater (bio)diversity so increase in predators of pests Disadvantage - 2. Reduced land area for crop growth

Question 37

Explain how human mass at birth is affected by stabilising selection (3 marks)

Answer 37

1. Extreme mass babies least likely to survive 2. to reproduce and so 3. less likely to pass on their alleles for extreme mass at birth

Question 38

The scientists calculated a P value of 0.03 when testing their null hypothesis. What can you conclude from this result? Explain your answer. (2 marks)

Answer 38

1. Probability that difference is due to chance is less than 0.05 2. Reject null hypothesis;

Question 39

Name one source of DNA from an extinct animal? (1 mark)

Answer 39

Bone/skin/preserved remains / museums;

Question 40

Other than hunting, suggest two reasons why populations might show very low levels of genetic diversity. (2 marks)

Answer 40

1. Population might have been very small/genetic bottleneck; 2. Population might have started with small number of individuals / founder effect; 3. Inbreeding;

Question 41

Explain why it is more useful to calculate an index of diversity than to record species richness. (2 marks)

Answer 41

1. Index of diversity also measures population size of each species 2. So useful because may be many of some species

Question 42

Suggest one reason the scientists used biomass instead of the number of individuals of each plant species when collecting data to measure diversity (1 mark)

Answer 42

too time consuming to count individuals

Question 43

Explain how the use of antibiotics has led to antibiotic-resistant strains of bacteria becoming a common cause of infection acquired when in hospital (3 marks)

Answer 43

1. some bacteria have alleles for resistance 2. resistant bacteria survive and reproduce 3. more antibiotics used in hospital

Question 44

Give three differences between DNA molecules and tRNA molecules? (3 mark)

Answer 44

1. Deoxyribose v ribose; 2. Double-stranded v single-stranded; 3. Many nucleotides v few ; 4. Thymine v uracil; 5. Double helix v clover (leaf structure); 6. Does not bind to amino acid v does bind to amino acid; 7. No exposed bases v anticodon;

Question 45

Suggest why amino acid replacement changes the properties of a protein? (2 marks)

Answer 45

1. changes the bond 2. which changes the tertiary structure

Question 46

The total number of bases in the DNA of the α-polypeptide gene is more than 423. Give two reasons why there are more than 423 bases. (2 marks)

Answer 46

- Non coding DNA - Addition of base by mutation

Question 47

Farmers clear tropical forest and grow crops instead. Explain how this causes the diversity of insects in the area to decrease. (3 marks)

Answer 47

1. Lower diversity of plants 2. Few sources of food 3. Few habitats/ niches;

Question 48

The spotted owl is a bird. Numbers of spotted owls have decreased over the past 50 years. Explain how this decrease may affect genetic diversity (2 marks)

Answer 48

1. Reduced (genetic diversity); 2. As fewer different alleles / reduced gene pool;

Question 49

State the function of the protein found in chromosomes (1 mark)

Answer 49

fixes the DNA into position

Question 50

Explain how the considerable length of a DNA molecule is compacted into a chromosome (1 mark)

Answer 50

looped and coiled a number of times

Question 51

Distinguish between a codon and an anticodon (2 marks)

Answer 51

1. codon is a triplet of bases of mRNA that codes for an amino acid 2. anticodon is the triplet of bases on a tRNA that is complementary to a codon

Question 52

Explin the advantage of DNA being a stable molecule (1 mark)

Answer 52

ensure genetic continuity between generations - genetically similar

Question 53

A strand of mRNA has 64 codons but the protein produced from it only has 63 amino acids. Suggest a reason why (1 mark)

Answer 53

one codon is a stop codon and they do not code for any amino acid

Question 54

The genetic code can be described as degenerate but not ambiguous. Explain why (2 marks)

Answer 54

1. most amino acids have more than one codon 2. however any one triplet only codes for a single amino acid

Question 55

Explain why the percentages of bases from the middle part of the chromosome and the end part are different (2 marks)

Answer 55

1. Different genes; 2. Have different (base) sequences 3. (Pre-mRNA) transcribed from different DNA

Question 56

Describe how two amino acids differ from one another (1 mark)

Answer 56

different R group

Question 57

Explain why errors in DNA replication can be far more damaging than errors in transcription (2 marks)

Answer 57

1. transcription usually only affects specific cells, are temporary and not inherited 2. errors in DNA replication may be inherited and may have permanent effect on whole organism

Question 58

A mutation was originally only found one one population in Central Asia. It is now found in many populations across Asia. Suggest how this spread occurred (1 mark)

Answer 58

migration

Question 59

Suggest reasons why a non-resistant bacteria was able to grow in a culture containing bacteria (2 marks)

Answer 59

1. mutation 2. contamination w/ other bacteria

Question 60

Two proteins have the same number and type of amino acids but different tertiary structures. Explain why. (2 marks)

Answer 60

1. Different sequence of amino acids 2. Forms ionic / hydrogen / disulfide bonds in different places;

Question 61

What is selection? (1 mark)

Answer 61

process by which organisms that are better adapted to their environment survive and breed, while those less well adapted fail to do so

Question 62

Suggest a reason why dinosaurs are not shown along the time line like all the other groups (1 marks)

Answer 62

dinosaurs are extinct but all other groups are still living

Question 63

It is very difficult to distinguish different species by fossils. Suggest two reasons why (2 marks)

Answer 63

1. fossils records can not reveal whether individuals can mate 2. often incomplete so not all features can be observed

Question 64

Suggest reasons why it is often difficult to distinguish organisms as separate species (3 marks)

Answer 64

1. fossil records are incomplete 2. species evolve over time so lots of variety 3. current classifications only reflect current scientific knowledge

Question 65

Explain why an increase in greenhouse gases is more likely to result in damage to communities with a low species diversity index than communities with a high index (2 marks)

Answer 65

1. community less likely to include a species adapted to withstand the change 2. therefore less chance of survival

Question 66

Explain what causes the DNA sequences of genes to change over a period of time (1 mark)

Answer 66

mutations

Question 67

List two reasons why a sample may not be representative of the population as a whole (2 marks)

Answer 67

1. sampling bias 2. chance variation

Question 68

The forest was cleared to make more land available for agriculture. After the forest was cleared the species diversity of insects decreased. Explain why (3 marks)

Answer 68

1. Decrease in variety of plants / fewer plant species; 2. Fewer habitats/niches; 3. Decrease in variety of food / fewer food sources

Question 69

What is meant be a hierarchy (2 marks)

Answer 69

1. Groups within groups; 2. No overlap (between groups)

Question 70

Scientists use protein structure to investigate the evolutionary relationships between different species. Explain why (2 marks)

Answer 70

1,2. More closely related (species) have more similarities in amino acid sequence/primary structure

Question 71

Comparing the base sequence of genes provides more evolutionary information than comparing the structure of proteins. Explain why (2 marks)

Answer 71

1,2. different base sequence codes for same amino acid

Question 72

Suggest how an increase rate of growth for a plant may increase profit (1 mark)

Answer 72

Plant ready quicker / less time required / allows land to be used again / harvested earlier;

Question 73

Other than hunting, suggest two reasons why populations might show very low levels of genetic diversity (2 marks/0

Answer 73

1. Population might have been very small/genetic bottleneck; 2. Population might have started with small number of individuals / by one pregnant female / founder effect; 3. Inbreeding;